Daniel M'Naghten attempted to kill the Prime Minister, Sir Robert Peel, but instead shot and killed Edward Drummond, the Prime Minister's Secretary. M'Naghten was suffering from insane delusions at the time of the killing. The House of Lords formulated the M'Naghten rules which apply in determining whether a person should escape criminal liability on the grounds of being insane.

Lord Tindal CJ:

"In all cases of this kind the jurors ought to be told that every man is presumed to be sane, and to possess a sufficient degree of reason to be responsible for his crimes, until the contrary be proved to their satisfaction: and that to establish a defence on the ground of insanity, it must be clearly proved that at the time of commiting the act the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing, or as not to know that what he was doing was wrong."